/*
    当前保留字

    break       do          in          typeof
    case        else        instanceof  var
    catch       export      new         void
    class       extends     return      while
    const       finally     super       with
    debugger    function    this
    default     if          throw
    delete      import      try
 */

/*
        未来保留字,也不可以使用
        enum

        严格模式下保留
        implements      package     public
        interface       protected   static
        let             private

        模块代码中保留
        await
 */
